Doliodrilus tener Erséus, 1984

Wang, Hongzhu & Erséus, Christer, 2004, New species of Doliodrilus and other Limnodriloidinae (Oligochaeta, Tubificidae) from Hainan and other parts of the north-west Pacific Ocean, Journal of Natural History 38 (3), pp. 269-299 : 272-274

Doliodrilus tener Erséus, 1984

(figure 1)

Doliodrilus tener Erséus, 1984: 159–160, figure 15; Erséus, 1990 a (partim): 287–288, figure 11A, B, E–G, I, J; Erséus et al., 1990: 113, figure 2K; Erséus and Hsieh, 1997: 100–101.

New material. IHB HANA2000003 b–e, HANA2000017 e, HANA2000022 a–e, HANA2000029 c–f, 14 specimens: four from SY00-2A, one from SY00-9C, five from Station HU00-14A, four from HU00-19A. SMNH Main Coll. 43665–43677, 13 specimens: three from SY00-2A, seven from HU00-14A, three from HU00-19A .

Brief description of new material. Six complete specimens 5.1–9.8 mm long, 28–45 segments. Diameter at XI about 0.4 mm. Prostomium usually conical. Clitellum extending over XI–XII. Chaetae 50–75 m m long, about 2.5 m m thick, with upper teeth 1–1.5 times as long as, and thinner than or as thick as, lower; two to five per bundle anteriorly, one to three per bundle in post-clitellar segments. Chloragogen cells from VI onwards. Oesophagus in IX barrel-shaped, thick-walled and granulated, with or without chloragogen cells; semi-embedded blood plexus permeating dorsal region, with regular transverse vessels and less regular longitudinal ones. Vasa deferentia (figure 1A: vd) about 135 m m long, 12–19 m m wide. Atria totally 200– 220 m m long, 14–36 m m wide; ental end of atrial ampullae thin-walled and distinctly dilated; ventral projections on ampullae either (1) triangular (figure 1A), each with small (only 10–17 m m long) prostatic pad (ppd) at bottom, and with numerous spindle-shaped nuclei (ncc) along both sides of pad (especially ental to pad), or (2) hemispherical (figure 1B), with large (29–34 m m long) prostatic pad (ppd), and with dense, but smaller patches of slender nuclei (ncc) around pad. Dense cluster of nuclei also present in dorsal wall of ampulla opposite to prostatic pad; these nuclei slender and regularly arranged when ventral projection triangular (figure 1A: nco), but oval and less regular when projection hemispherical (figure 1B: nco). Prostate glands (figure 1A, B: pr) usually medium to large, sometimes small, with small nuclei and large nucleus-like bodies, latter oblong to round, maximally 12 m m long, 11 m m wide. Atrial ducts (figure 1A, B: ad) each with (1) posterior blind sac (bs), 25–50 m m long, 15–30 m m wide, and (2) efferent duct (ed), 25–35 m m long, 19–27 m m wide. Sperm sac in one to five segments within IX–XIII, when developed at all. Egg sac in one to three segments within XI–XIII, when developed. Spermathecal ducts 45–95 m m long, 24–44 m m wide, with ectal vestibules; ampullae 85–175 m m long, 30–95 m m wide, with sperm arranged in bundles or masses in lumina.

Remarks. This species was originally described from Hong Kong (Erséus, 1984). In 1990, Erséus reported it from Hong Kong again, noting some morphological variation, but a form with unusually long upper teeth on the chaetae is now regarded as a separate taxon (see D. longidentatus sp. n. below). The other known distributional areas of D. tener are Qingdao (Erséus et al., 1990) and Taiwan (Erséus and Hsieh, 1997).

The most prominent character of D. tener, not specifically noted in the previous descriptions, is the conspicuous thickening of the dorsal wall opposite to the prostatic pad in the atrium, and the clusters of nuclei in this wall and around the pad. We observed this character in all the material from Hainan, as well as in numerous old specimens from Hong Kong [treated by Erséus, 1984, 1990 a (partim)]. However, there are two different appearances of the ventral projections on the atria; they are either triangular (figure 1 A) or hemispherical (figure 1 B) (see above description). In the former state, the small prostatic pads seem to have discharged secretion into the atria, and the nuclei around the pads are widely distributed. In the latter state, the large pads appear to be full of secretion, and the nuclei are more restricted in distribution.

The prostate glands were stated to be small in the Hong Kong material (Erséus, 1984, 1990a), but a re-examination shows that the glands in the specimens from Hong Kong and Taiwan (Erséus and Hsieh, 1997), as well as in the new material, vary considerably, i.e. from small to large.

Distribution and habitat. Known only from China [Hainan (new record), Hong Kong, Jiaozhou Bay (at Qingdao), Taiwan]. Brackish-water, intertidal and subtidal soft mud and muddy sand.